This invention relates generally to a downshift and override control for a work machine utilizing a hydrostatic transmission having one or more motors and more particularly to automatically downshifting the one or more motors in response to input related to a parameter within the hydrostatic transmission.
Currently, hydrostatic transmissions are used for propelling a wide variety of machines, including, but not limited to, small tractors, combines, skid steer loaders, and wheel loaders, under low to high travel speed conditions. Advantages of the hydrostatic transmissions include efficiency at low speeds and ability to infinitely vary speed within the speed range under load without clutching. However, hydrostatic transmissions have been found to be inefficient at high travel speeds for operating certain functions of the work machine. For example, reverse track steering requires the highest torque capability from the hydrostatic transmission. A certain amount of torque is necessary when the work machine is traveling within the high speed range which reduces the torque availability for reverse track steering. Further, a control lever is used for directing the travel of the work machine in either a forward or reverse direction. It is sometimes beneficial to have increased modulation of the control lever when traveling in the reverse direction for improved operator control/performance. However, a certain amount of hydraulic fluid flow is diverted from the control lever when the work machine is traveling in the high speed range, thus reducing modulation capability of the control lever.
In order to overcome these concerns, it is well known to provide a two speed switch on the control lever located within a cab of the work machine. An operator may choose to reduce the travel speed of the work machine by manually operating the switch to actuate a two speed control valve for reducing the one or more motors to the low speed range. Alternatively, when the operator desires to increase the travel speed to the high speed range, the switch is manually operated to actuate the two speed control valve for increasing the one or more motors to the high speed range. As can be easily understood, such manually input by the operator may be inconsistent and cause inefficient operation of the work machine. Further, such manually input requires constant vigil by the operator to ensure that the most efficient speed range is selected which increases time and energy spent by the operator. Therefore, it would be beneficial to provide an automatic downshift control during certain work conditions, such as, reverse track steering or reverse drive along with the manual input capability.
The present invention is directed to overcome one or more of the problems as set forth above.
In one aspect of the present invention, a hydrostatic transmission system comprises a source of hydraulic fluid. A pump is used for pressurizing the hydraulic fluid. A motor group is connected with the pump for receiving the pressurized hydraulic fluid. The motor group has a defined speed range for driving an output in either forward or reverse directions. Means is connected between the pump and the motor group for controlling the displacement of the motor group. A control mechanism is used for determining the pressure of the hydraulic fluid and for directing the controlling means in response to a specific pressure determination that relates to the direction that the motor group is driving the output to selectively change the displacement of the motor group and achieve a predetermined speed within the speed range.
In another aspect of the invention, a method is disclosed for automatically changing the speed of a motor group having forward and reverse drive conditions. The motor group is located within a transmission system for a work machine. The method comprises the steps of determining whether the motor group is in the reverse drive condition and automatically changing the speed of the motor group from a high speed to a low speed in response to the reverse drive condition.
In yet another aspect of the invention, a hydrostatic transmission system for a work machine comprises a source of hydraulic fluid. A pump is used for pressurizing the hydraulic fluid. A motor group is connected with the pump for receiving the pressurized hydraulic fluid. The motor group has high and low speeds for driving an output in either forward or reverse directions. A control mechanism is used for determining when the motor group is driving the output in a reverse direction and for automatically changing the speed of the motor group to the low speed in response to the determination.
In yet another aspect of the invention, a hydrostatic transmission system for a work machine comprises a source of hydraulic fluid. A pump is used for pressurizing the hydraulic fluid. A motor group is connected with the pump for receiving the pressurized hydraulic fluid. The motor group has a defined speed range for driving an output in either forward or reverse directions. A control device is connected with the motor group and is selectable to send a speed signal to the motor group for driving the output at a predetermined speed within the speed range. A sensing device is disclosed. A controller is connected with the control and sensing devices and is used for sending a control signal in response to a predetermined speed signal and predetermined input from the sensing device to automatically override the selected speed signal from the control device.
The present invention includes a hydrostatic transmission that has a control device that is selectable to send a speed signal to a motor group for driving an output at a predetermined speed. A controller is used to automatically override the selected speed signal in response to a predetermined speed signal and predetermined input from a sensing device. This invention allows for the speed of the motor group to be changed from a high speed to a low speed when the motor group is driving the output in a reverse direction to achieve greater efficiency and control of a work machine.